VIBRATIONAL-SPECTRA OF XANTHIONE AND XANTHONE

The fundamental vibrational frequencies of xanthione (XT) and xanthone (XN), two structurally turally similar heteroaromatic molecules, have been obtained experimentally using FTIR and Raman spectroscopy. Ab in itio RHF/STO-3G* and RHF/CEP-31G and semiempirical RHF/AM1 and RHF/PM 3 molecular orbital calculations have been performed to obtain the vib rational frequencies of these molecules from their force fields. A com parison of the experimental and calculated frequencies reveals that al l four theoretical methods overestimate the vibrational frequencies an d that the rms deviations increase in the order CEP-31G < STO-3G* < P M3 < AM1. The frequencies obtained by the effective core potential, CE P-31G, method are in excellent agreement with experiment when the calc ulated frequencies are scaled uniformly by a factor of 0.8953. (C) 199 5 Academic Press, Inc.